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DM in Labs

I was doing some pedigree research and clicked on a link to a website for one of the dogs. The bio on this dog said he died from Degenerative Myelopathy. He died only a few years ago. I have no idea what testing was done to diagnose the dog. I'm wondering how accurate a diagnosis of DM in a Labrador is. Does DM often go undiagnosed in labs? Does it present in Labs differently or commonly later than other breeds it is more prevalent? I've read some things on the DDC website that offers DM testing and info on the OFA website. It seems inheritance is simple, recessive (like eic) and is not all that common in Labs according to the current statistics. If this dog was accurately diagnosed and was affected by DM, his sire had to be at least a carrier, correct?His sire was one of the most prolifically bred Labs in history. Not sure if this is common knowledge and I just missed it. But I don't see many testing for DM in Labs and of this dog's sire was a carrier, many of us are likely to have carriers.

Many Chesapeakes are now tested for DM, not sure about Labs. One of the big problems w/ DM is that, in general, it can often go undiagnosed or misdiagnosed. Generally a definitive diagnosis can only be made post-mortem. I would be curious about testing of Labs (and other retriever breeds) too.

Before the DNA test some thought Degenerative Myelopathy to exist in Labradors but Labradors do not have the DM gene mutation so if it exists in Labradors it is a different gene. As was previously stated a definitive diagnosis of DM could only be made post mortem but the DNA test has improved diagnosis. Any diagnosis of degenerative myelopathy based on clinical symptoms only is erroneous. There is little doubt that a degenerative NEUROPATHY exists in Labradors and includes some or all of the following, laryngeal paralysis, megasophagus, and posterior weakness and proprioception deficits but this, as yet unnamed syndrome, is not degenerative myelopathy.

Before the DNA test some thought Degenerative Myelopathy to exist in Labradors but Labradors do not have the DM gene mutation so if it exists in Labradors it is a different gene. As was previously stated a definitive diagnosis of DM could only be made post mortem but the DNA test has improved diagnosis.

Not trying to be smart, but why does OFA show that some Labs have tested to be "at risk" and "carrier" of DM though the genetic test? Are those false positives?

And if a dog is affected by DM, does it mean sire and dam were at minimum carriers (possibly affected)?

Chesapeakes are one of several breeds with a much higher incidence of DM than the canine population in general. Most CBR breeders test for it and avoid breedings that may produce at risk pups; awareness was heightened due to the death from DM of 2 prominent sires, both Dual Champions. Many long time breeders agree they may well have had dogs with DM that they just assumed gradually lost use of their back end because of age/arthritis. As was mentioned by EdA & riskyriver there is no way to definitively diagnose DM except by necropsy. The genetic test for DM is fairly new; only about 5 years old and it tests for only one of several genes thought to be involved in the disease. Some dogs that have tested "at risk" may not come down with the disease; other at risk dogs may get it so late in life that they die of something else before the DM progresses.

I've never heard of Labs being mentioned amongst the breeds that have a higher than normal incidence of DM; it's a very rare disease in all but a few breeds. I'm not sure why people would even test Labs for DM, except that there is a test available and some people want to test their dogs for every single thing that can be tested. In answer to your question, in order for a dog to inherit 2 copies of the gene the dog would need to get one from each parent, so either both were carriers, one was a carrier, one at risk, or both were at risk. Note that for DM, a dog with 2 copies of the gene is not called "affected" it is classified as at risk since not all will get the disease.

Another note regarding the DNA test. Dogs have been reported as affected by DM that tested as "carriers," possessed of one normal copy of the gene targeted by the test. I'm not sure if there have been "clears" affected. So not only is the gene targeted by the test just one of a number of genes affecting the disorder, the test is not a certain predictor of either disease or disease-free status.

Another note regarding the DNA test. Dogs have been reported as affected by DM that tested as "carriers," possessed of one normal copy of the gene targeted by the test. I'm not sure if there have been "clears" affected. So not only is the gene targeted by the test just one of a number of genes affecting the disorder, the test is not a certain predictor of either disease or disease-free status.

While it's true that there are reports of two or three carrier dogs (actually I think it was 2 carrier, and one clear) that were diagnosed with DM, it is important to note that these cases were genetically different (and extremely rare) forms of DM. Regrettably, there are some people using those reports as an excuse to pump out litters of puppies at risk for DM. Right now the existing test is all we have. Clearly, more research is needed, especially of older at risk dogs that do not have DM. While I happen to be one that believes it would be a mistake to avoid ALL breedings that have the potential to produce at-risk puppies, I also believe that those breedings should only be done when the parents are of exceptional quality and bloodlines that cannot be found elsewhere. And the risk factor should be fully disclosed to all puppy buyers--something that, sadly, is not happening. If it is mentioned at all, reports such as the one in quotes are glibly trotted out as an excuse for the irresponsibility of producing such puppies.

I don't know the numbers. I am in the process of submitting a tissue sample to the researchers at the University of Missouri (yes I am mourning the loss of a beloved dog) and Dr. Hansen told me they have seen changes typical of DM in the spinal cords of dogs that tested as carriers.

I would agree it is not desirable to give people excuses for careless breeding, but I also think it is very important to be aware of the limitations of these DNA tests and resist the tendency to be dogmatic about them. I believe in what testing has to offer, enough to send an animal I have loved for 16 years off to be cut up instead of giving her a quiet burial. But I also see great destructive potential in the rush to limit selection of breeding stock based on yet another test.